<!DOCTYPE html>
<style>
  body {
    will-change: transform;
  }
  #container {
    height: 300px;
    width: 300px;
    background-color: green;
    will-change: transform;
  }

  #parent {
    position: absolute;
    left: 400px;
    width: 300px;
    height: 300px;
    background-color: green;
    -webkit-transform-style: preserve-3d;
  }
  
  #child {
    position: absolute;
    width: 200px;
    height: 200px;
    z-index: -2;
    background-color: red;
    will-change: transform;
  }
</style>
<body>
<div id="container">
  <div id="parent">
    <div id="child"></div>
  </div>
</div>
<script>
if (window.testRunner)
  testRunner.waitUntilDone();

requestAnimationFrame(function() {
  requestAnimationFrame(function() {
    document.getElementById('parent').style.webkitTransformStyle = 'flat';
    setTimeout(function() {
      testRunner.notifyDone();
    });
  });
});
</script>
</body>
